Ball bearing slide with synchronizing mechanism

ABSTRACT

A drawer slide structure in which two mating slide rails oppositely enclose an intermediate member which carries a roller peripherally extending into longitudinal runways formed in the rails, the runway floors presenting surfaces of one material for pressure engagement by the peripheral surface of another material presented by the roller, the two materials being of such character as to establish a driving connection inhibiting slippage therebetween. In the optimum form, the two materials are of the type known as &#39;&#39;&#39;&#39;VELCRO&#39;&#39;&#39;&#39; brand hook and loop tape, and preferably the hook type tape is on the roller while the loop type tape is on the runway floors, though that relationship may be reversed. Alternatively, one of the materials may be relatively soft and elastically deformable by the other material which is relatively hard and crenelated or otherwise roughened.

United States Patent Fall et al.

[54] BALL BEARING SLIDE WITH SYNCHRONIZING MECHANISM [72] Inventors: Herbert S. Fall, 6248 E. lona Road, lndianapolis, lnd. 46203; William D. York, 50 West Edwards Ave., Indianapolis, Ind. 46217; Larry D. Huff, 1130 North Chester Ave., Indianapolis, Ind. 46201 [73] Assignee: said Fall, by said York and said Huff [22] Filed: June 11, 1971 [21] Appl. No.: 152,258

[52] [1.8. CI ..308/3.8, 312/332, 312/341 NR, 3 l2/348 [51] Int. Cl. ..Fl6c 29/00 [58] Field oiSeaIch ..308/3.8; 312/340, 341,341 NR, 312/348, 332, 334

[45.1 July 25, 1972 727,787 4/l9 65 Great Britain ..308/3.8

Primary Examiner-Martin P. Schwadron Assistant Examiner-Barry Grossman Atlorney-Hood, Gust, lrish, Lundy & Coffey [5 7] ABSTRACT materials are of the type known as VELCRO" brand hook and loop tape, and preferably the hook type tape is on the roller while the loop type tape is on the runway floors, though that relationship may be reversed. Alternatively, one of the Reiel'ences cited materials may be relatively soft and elastically deformable by the other material which is relatively hard and crenelated or UNITED STATES PATENTS otherwise roughened. I

3.8 3,488,097 1/1970 Fall 308/ 13 Claims 8 Drawing Figures FOREIGN PATENTS R APPLICATIONS 1,457,675 9/1966 France ..308/3.8

PATENTEDwmsmn BEST AVAILABLE 3.679275 sum 1 ur INVENTORS HERBERT 3. FALL 3 i WILLIAM D. YORK LARRY D. HUFF 8- W M ZYMM f ATTORNEYS PATENTEDmas m2 B15311 AVAKABLE COPY 3.679.275

'sum 2 or 2 INVENTORS HERBERT s. FALL WILLIAM D. YORK LARRY n. HUFF BY MMMz z ATTORNEYS BALL BEARING SLIDE WITI-I SYNCI-IRONIZING MECHANISM The present invention relates to a ball bearing slide with synchronizing mechanism and is directed primarily to the provision of heavy duty means for supporting a structure during movement of that structure between what may be referred to as a rest position, and one or more extended positions, which extended positions may be oppositely spaced from the rest position of the structure. A primary object of the invention is to provide, in such a mechanism, inexpensive, readily applied, longlived means for ensuring the maintenance of a balanced condition among the several parts of the slide structure.

Further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, our invention may be embodied in the forms illustrated in the accompanying drawings, attention being called to-the fact, however, that the drawings are illustrative only, and that change may be made in the specific constructions illustrated and described, so long as the scope of the appended claims is not violated.

FIG. 1 is a fragmental, isometric view of one end of a slide structure constructed in accordance with the present invention, showing the structure in partially extended condition;

FIG. 2 is an enlarged, fragmentary elevational view of a mid portion of the assembly illustrated in FIG. 1, parts being broken away for clarity of illustration;

FIG. 3 is a transverse section taken substantially on the line 3-3 of FIG. 2;

FIG. 4 is an enlarged, isometric view of a fragment of a bridge member, illustrating details of a journal mounting for a roller which is an important feature of our invention;

FIG. 5 illustrates a fragment of a back plate, showing one form of material which may be used as a runway floor surface in accordance with our invention;

FIG. 6 is a sectional view somewhat diagrammatically illustrating a roller in cooperative engagement with runway surfaces of the character illustrated in FIG. 5;

FIG. 7 is a fragmentary, exploded, somewhat diagrammatic illustration of a back plate provided with a different form of runway floor material and a bridge member carrying a roller whose peripheral surface is covered with still another kind of material for cooperation with the runway floor material; and

FIG. 8 is a view similar to FIG. 6 but showing the floor and roller surface materials of the kinds suggested in FIG. 7.

Referring more particularly to FIG. I, it will be seen that we have illustrated a fragment of a three-member slide rail structure. When such a structure is used at each side of a drawer member to support that drawer member for outward and inward movement relative to a frame, the rail 10 may be suitably secured to one side of a drawer opening in a frame while the second rail 11 is secured to one side of the drawer structure to support the same, an intermediate member 12 being interposed, and providing an operative connection, between the first and second rails 10 and 11. The intermediate member 12 is suitably retained for longitudinal reciprocation only relative to the rail 10, and the rail 11 is suitably retained for longitudinal sliding movement only with respect to the intermediate member 12. Slide structures of this general character, as thus far described, are well known in the art to which the present invention pertains; and our invention resides in the details of structure to be described, whereby the slide structure is improved, its manufacture, assembly and maintenance are rendered more economical and maintenance of a balanced condition among the three major parts of the slide structure is significantly improved.

As will be perceived from a careful examination of FIGS. 1, 2 and 3, the rail 10 comprises a first elongated channel element 13 of C-shaped cross section and a second elongated channel element 14 of C-shaped section arranged in transversely-spaced parallelism with the channel element 13 to define a parallel runway 15 therebetween. The channel elements 13 and 14 are spanned and joined by a back plate 16 which may be spot welded to the backs of the elements 13 and I4 and is preferably longitudinally coextensive therewith. A stop bar l7 blocks one end of the runway 15 and a similar stop bar (not shown) blocks the opposite end thereof.

The longitudinal edges of the channel element 13 are shaped to provide a curled lip 18 defining a longitudinal trackway l9 and an oppositely curled lip 20 defining a trackway 21 facing the trackway 20. Similarly, the channel member 14 has its edges shaped to provide a curled lip 22 defining a trackway 23 and a curled lip 24 defining a facing trackway 25.

A generally U-shaped ball bearing cage 26 of known construction carries a series of balls 27 at one side retentively enterable in the trackway 19 and carries a series of balls 28 at its opposite side retentively receivable in the trackway 21, whereby said cage is retained in the channel 13 for longitudinal reciprocation only relative thereto. A similar cage 29 provided with a series of balls 30 and a series of balls 31 is similarly retained for reciprocation only in the channel element 14 with its balls 30 in the trackway 23 and its balls 31 in the trackway 25.

The rail 11 is identical, but allochirally arranged with respect to the rail 10. As is most clearly to be seen in FIG. 3, the rail 11 comprises a C-shaped channel 33 and a C-shaped channel 34 arranged in parallelism to define a parallel runway 35 therebetween. A back plate 36 spans and is preferably spot welded to the back surfaces of the channel members 33 and 34 and a stop bar 37 blocks one end of the runway while a similar stop bar (not shown) blocks the other end of the runway. The channel member 33 is fonned to provide a curled lip 38 defining a trackway 39 and a curled lip 40 defining a trackway 41 facing the trackway 39. The channel member 34 is formed to provide a curled lip 42 defining a trackway 43 and a curled lip 44 defining a trackway'45 facing the trackway 43. A cage 46 having a series of balls 47 retentively received in the trackway 39 and a series of balls 48 retentively received in the track-way 41 is thus retained for longitudinal reciprocation only in the channel member 33; while a similar cage 49 is similarly retained in the channel member 34 by engagement of its balls 50 in the trackway 43 and engagement of its balls 51 in the trackway 45. 1

The intermediate member 12 consists of four identical bars 52, 53, 54 and 55. The bars 52 and 53 are secured together back to back to form a leg and the bars 54 and 55 are secured together back to back to form a similar leg; and a bridge piece 56, interposed between the bar pairs, spans and joins the legs substantially at their centers of length. As will appear more fully hereinafter, the lateral edges of the bridge piece may be substantially coincident in lengthwith the legs of the intermediate member l2, or separate spacer pieces (not shown) may be interposed between the bars of each leg to prevent bar warpage.

Each of bars 52, 53, 54 and 55 is formed to provide, at its lateral edges, parallel, longitudinal lips 57 and 58 shaped to define outwardly presented trackways 59 and 60 so located, when the parts are assembled, as retentively to receive the ball series 27 and 28, respectively, or the corresponding series of the associated cage. It will be perceived that, with the stops blocking the ends of the runways removed, the intermediate member 12 can be telescoped into both of the rails 10 and 11, thus engaging the balls of the several cages, whereby the assembly of three major parts will be completed.

The ball bearing cages 26, 29, 46 and 49 may be of the character illustrated, in which each ball of each series is received in its individual pocket and longitudinally spaced from every other ball of the series, or they may be of the type in which only the terminal balls of a series are held in individual pockets spaced apart at a fixed distance, while the intermediate balls of the series are longitudinally restrained only by each other and by the terminal balls. The two types are commercially known and, so far as the present invention is concerned, are interchangeably usable to connect the several major elements of the assembly for relative longitudinal move ment only.

Of course, the expression ball bearing cage" as used herein refers to the complete assembly including not only the pocketforming, restraining device but also the series of balls restrained thereby.

Quite obviously, when the parts as thus far described are so assembled and the rail 11 is moved toward the left, for instance, while the rail is held stationary, the intermediate member 12 may or may not be entrained to an indeterminate extent; and when the rail 11 reaches full registry with the rail 10, the intermediate member 12 may have trailed behind the rail 11 and thus be left protruding from the right-hand end of the assembly, or it may have preceded the rail 1 1 and so be left protruding from the left-hand end of the assembly. Such conditions are patently undesirable, and further it is desirable that the three major elements of the assembly remain in balanced condition at all times during the complete path of movement of the drawer or other structure supported by the slide assembly. It is thus a major objective of the present invention to provide novel, inexpensive and highly effective means to enforce the desired relative movement among the three major elements of the assembly.

To that end, we mount upon the intermediate member 12 a roller or rotor 66 so located, proportioned and designed as to extend peripherally into both of the runways 15 and 35. Each runway is so constructed that its floor presents a surface of one kind of material and the roller periphery is so constructed as to present a surface of a different kind of material cooperative with the runway floor material to establish a highly effective driving connection between the runway surfaces and the roller surface.

Because of the functions assigned to these parts, and because of the limited space available for the mounting of such a rotor, the details of that mounting become quite important.

Referring to FIG. 4, it will be seen that our bridge piece 56, which must be quite thin in a direction perpendicular to the runway floors, is a piece of sheet material. We have found thin sheet steel to be an acceptable material, but we believe that sheet brass or bronze could be used and that some of the synthetic plastic sheets might also be used. Desirably, the material of the bridge piece should be resiliently flexible for a reason which will appear.

As shown in FIG. 4, the bridge piece comprises a longitudinally extending base 61 formed with an opening 64 therethrough to define longitudinally-spaced legs 62 and 63. The base 61 of the bridge piece 56 is disposed between, and suitably secured to, one of the pairs of bars, for instance 54 and 55, of the intermediate member 12. As has been indicated, the length of the base 61 may be substantially coincident with the length of the leg pair between which it is disposed, or it may be only of sufficient length to support the longitudinally spaced legs 62 and 63, in which case separate spacer pieces will be arranged between the bars 54 and 55 on both sides of the bridge piece.

The legs 62 and 63 extend from the base 61 with their distal end regions disposed between the other bar pair, for instance,

52 and 53 and are there secured to the bars. Here, again, integral, longitudinal extensions from the distal ends of the legs 62, 63 may continue to the opposite ends of the bar pair, or separate spacers (not shown) may be arranged between the bars on opposite sides of the base piece.

At a point preferably mid-way between the legs 62, 63, a finger 65 extends from the base 61 into the opening 64. Near the distal end of the finger 65, a substantially half round bar 68 is welded to one face of said finger and a mating, similar bar 69 is welded to the opposite face of said finger in registry with the bar 68. The radius of curvature ofeach bar is at least equal to one-half the width of the finger 65 and the radial dimension of each bar measured in a direction perpendicular to the faces of the finger is less than the radius of curvature by one-half the thickness of the finger 65. Thus, the bars 68 and 69, when secured to the finger, cooperate to define a cylindrical axle having a diameter substantially equal to the internal diameter of the axial bore 67 of the roller 66 which is joumalled on said axle. Preferably, of course, the roller 66 includes anti-friction means (not shown) directly joumalled on the axle.

While we have shown the bars 68 and 69 of such radial curvature that the axle diameter is substantially equal to the width of the finger 65, it will be apparent that they may be larger, but cannot be smaller.

The parts are so proportioned and designed, and the roller 66 is so positioned on the finger 65, that when the parts are assembled, the roller 66 peripherally extends into, and is guided by the runways l5 and 35 and into pressure engagement with the surface materials of the floors of both runways. Because of the inherent resilient flexibility of the material from which the bridge piece is formed, the finger 65 is sufficiently resiliently flexible to permit the roller to maintain pressure engagement with the runway floor surfaces in spite of any minor unevennesses in such floor surfaces.

Various pairs of surface materials are available for use on the runway floors and the peripheral surface of the roller. Thus, for instance, in FIG. 3 we have shown rubberoid strips 70 secured to the runway floors and cooperating with 71 is metal which has been roughened, knurled or otherwise with a roller whose peripheral surface 6, we have shown expanded metal stripes 74 secured to the runway floor and cooperating with a roller 66 whose peripheral surface is rubberoid material 7 We presently believe, however, that optimum materials for this use are as illustrated in FIGS. 7 and 8 in which each runway floor bears a strip 76 of fabric covered with a multiplicity of soft, tiny loops, while the peripheral surface of the roller bears a strip 77 of fabric covered with a multiplicity of stiff little hooks which retentively interengage with said loops when the two materials are pressed together. A characteristic of those materials is that, when so pressed together, they strongly resist separation by forces applied in a direction parallel to the interface or in a direction perpendicular to the interface, but may readily be separated by peeling" forces.

Such materials are available on the open market from VEL- CRO Corp., with otfices at 681 Fifth Avenue, New York City in the United States and from Canadian Velcro, Ltd. with offices at 1 14 East Drive, Bramalea, Ontario in Canada, and are known as VELCRO" brand hook and loop tape fasteners, and they are described in detail in a six-page brochure published by the former corporation, and a print of which is attached hereto.

It will be perceived that, as relative longitudinal movement occurs between the rails 10 and 11 and the intermediate member 12, the roller 66 with its strip 77 will rotate upon its axle while the strip 77 is in pressure contact with the strips 76 of the two runways l5 and 35. As the roller turns, points on its peripheral surface will be pressed against successive points of the runway floor surfaces to produce the above-mentioned interengagement of hooks with loops to establish firm driving connections between the roller surfaces and the runway floor strips; but it will also be perceived that, as those successive points move away from the roller, the rotation of the roller produces a peeling" action which readily disengages the hooks from the loops.

While reasonably satisfactory results are achieved with the cooperating materials of FIGS. 3 and 5 and 6, we have found that the form illustrated in FIGS. 7 and 8 is more effective against slippage and is longer-lived and therefore appears to be optimum.

It will be apparent that the illustrated assembly is of such character that it may be extended in either longitudinal direction from its completely collapsed condition. Of course, when the assembly is to be used as a drawer slide, one of the rails 10 or 11 will be fixedly mounted upon a frame while the other rail will support the drawer. The assembly can be used in other environments, such as, for instance, in an extensible table in which opposite end portions move concurrently away from a central support in opposite directions, in which case the intermediate member 12 will be secured to the frame, one leaf or end portion will be secured to one of the rails and the other leaf or end portion will be secured to the other rail. In such an environment, when one leaf or end portion is pulled away from the frame, the other leaf or end portion will automatically move, at the same rate, in the opposite direction away from the frame.

We claim:

l. A device of the class described comprising a first rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, a second rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, said channels and runway of said second rail being arranged in facing registry with the channels and runway of said first rail, an intermediate member having parallel legs slidably received respec tively in the channels of both rails, a bridge member joining said legs substantially at their centers of length, a roller journalled on a transverse axis on said bridgemember with its periphery extending into both of said runways, and an elongated ball bearing cage retained in each of said channels for longitudinal reciprocation therein, each cage further having retaining engagement with one of said legs, the floor of each runway presenting a surface of one kind of material and the peripheral face of said roller presenting a surface of another kind of material engaging and cooperating with said runway surfaces to inhibit slippage of said roller relative to said runway floors.

2. The device of claim 1 in which one of said materials is resiliently deformable and the other of said materials is rigid and roughened.

3. The device of claim 1 in which one of said materials is rubberoid and the other is metallic and crenelated.

4. The device of claim 1 in which said runway floor surface material is rubberoid and said roller peripheral surface material is roughened metal.

5. The device of claim 1 in which said runway floor surface material is expanded metal and said roller peripheral surface material is rubberoid.

6. The device of claim I in which one of said materials is a fabric covered with a multiplicity of stilT little hooks and the other of said materials is a fabric covered with a multiplicity of tiny, soft loops with which such hooks retentively interengage when the two materials are pressed together.

7. The device of claim 6 in which said one material constitutes the roller peripheral surface and said other material constitutes the runway floor surfaces.

8. A device of the class described comprising a first rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, a second rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, said channels and runway of said second rail being arranged in facing registry with the channels and runway of said first rail, an intermediate member having parallel legs slidably received respectively in the channels of both rails, a bridge'member joining said legs substantially at their centers of length, a rotor journalled on a transverse axis on said bridge member with its periphery extending into both of said runways, an elongated ball bearing cage retained in each of said channels for longitudinal reciprocation therein, each cage further having retaining engagement with one of said legs, and means including said rotor for enforcing relative longitudinal movement between said first rail and said intermediate member in one direction and at the same rate as a consequence of relative longitudinal movement between said second rail and said intermediate member in the opposite direction.

9. In combination, a first elongated member providing longitudinal guide means and a parallel runway, a second elongated member providing corresponding longitudinal guide means and a corresponding runway, an intermediate member providing slide means retentively received in both guide means for relative longitudinal movement, roller means journailed on said intermediate member and peripherally extending into said runways, a face of each runway presentin a surface of one kind of material and said roller means perip erally presenting a surface of another kind of material, one of said materials being a fabric covered with a multiplicity of stiff little hooks and the other of said materials being a fabric covered with a multiplicity of tiny, soft loops with which such hooks retentively interengage when the two materials are pressed together, said parts being so constructed and arranged that a rolling, pressure engagement is maintained between said roller means surface and said runway surfaces during relative longitudinal movement of said three members.

10. In a device of the class described, a first rail providing longitudinal guide means and a parallel runway, a second rail providing corresponding longitudinal guide means and a corresponding runway, an intermediate member providing slide means retentively received in the guide means of both rails for relative longitudinal reciprocation, a roller journalled on said intermediate member with its periphery extending into said runways, the floor of each runway presenting a surface of one kind of material and the peripheral face of said roller presenting a surface of another kind of material, one of said materials being a fabric covered with a multiplicity of stiff little hooks and the other of said materials being a fabric covered with a multiplicityof tiny, soft loops with which such hooks retentively interengage when the two materials are pressed together, said parts being so constructed and arranged that said roller face maintains a rolling, pressure engagement with both of said floors during relative longitudinal movement of said rails and intermediate member.

11. The combination of claim 9 in which the surface material of said runways is the loop type while the surface material of said roller means is the hook type.

[2. The device of claim 1 in which said bridge member is secured at its opposite edges to said legs, respectively, and having an intermediate opening therethrough, a finger integral with one lateral edge of said opening and extending into said opening with its distal end free, said roller having a concentric bore whose diameter is at least equal to the width of said finger, and two substantially half-round blocks fixed to the opposite faces of said finger, respectively, the radii of said blocks, measured in directions perpendicular to said faces, being equal and, in sum, less than the diameter of said bore by approximately the thickness of said finger, said roller being sleeved on said blocks to define the journal mounting for said roller.

13. The device of claim 12 in which said bridge member is a resiliently flexible sheet.

mg? UNITED STATES PA NT-wuss fiER-TIFICATE' OF C'DRRECTIO-N Datent No. 3,679,275 Dated July 25, 1972 lnventor'( 's) Herbert s Fall, William D; York and Larry D. Huff It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r On the title page, the address of Larry D. Huff should be changed from "1130 North Chester Ave." to 1320 North Chester Ave Column 4, rewrite lines 20-22, both inclusive, to read 70 secured to the runway floors and cooperating. with a roller whose peripheral. surface 71-. is metal which has been roughened, knurled or otherwise crenelated. In Figs. 5 and 6, we have shown expanded Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.F'LETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A device of the class described comprising a first rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, a second rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, said channels and runway of said second rail being arranged in facing registry with the channels and runway of said first rail, an intermediate member having parallel legs slidably received respectively in the channels of both rails, a bridge member joining said legs substantially at their centers of length, a roller journalled on a transverse axis on said bridge member with its periphery extending into both of said runways, and an elongated ball bearing cage retained in each of said channels for longitudinal reciprocation therein, each cage further having retaining engagement with one of said legs, the floor of each runway presenting a surface of one kind of material and the peripheral face of said roller presenting a surface of another kind of material engaging and cooperating with said runway surfaces to inhibit slippage of said roller relative to said runway floors.
 2. The device of claim 1 in which one of said materials is resiliently dEformable and the other of said materials is rigid and roughened.
 3. The device of claim 1 in which one of said materials is rubberoid and the other is metallic and crenelated.
 4. The device of claim 1 in which said runway floor surface material is rubberoid and said roller peripheral surface material is roughened metal.
 5. The device of claim 1 in which said runway floor surface material is expanded metal and said roller peripheral surface material is rubberoid.
 6. The device of claim 1 in which one of said materials is a fabric covered with a multiplicity of stiff little hooks and the other of said materials is a fabric covered with a multiplicity of tiny, soft loops with which such hooks retentively interengage when the two materials are pressed together.
 7. The device of claim 6 in which said one material constitutes the roller peripheral surface and said other material constitutes the runway floor surfaces.
 8. A device of the class described comprising a first rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, a second rail providing two transversely spaced, longitudinally parallel channels with a parallel runway therebetween, said channels and runway of said second rail being arranged in facing registry with the channels and runway of said first rail, an intermediate member having parallel legs slidably received respectively in the channels of both rails, a bridge member joining said legs substantially at their centers of length, a rotor journalled on a transverse axis on said bridge member with its periphery extending into both of said runways, an elongated ball bearing cage retained in each of said channels for longitudinal reciprocation therein, each cage further having retaining engagement with one of said legs, and means including said rotor for enforcing relative longitudinal movement between said first rail and said intermediate member in one direction and at the same rate as a consequence of relative longitudinal movement between said second rail and said intermediate member in the opposite direction.
 9. In combination, a first elongated member providing longitudinal guide means and a parallel runway, a second elongated member providing corresponding longitudinal guide means and a corresponding runway, an intermediate member providing slide means retentively received in both guide means for relative longitudinal movement, roller means journalled on said intermediate member and peripherally extending into said runways, a face of each runway presenting a surface of one kind of material and said roller means peripherally presenting a surface of another kind of material, one of said materials being a fabric covered with a multiplicity of stiff little hooks and the other of said materials being a fabric covered with a multiplicity of tiny, soft loops with which such hooks retentively interengage when the two materials are pressed together, said parts being so constructed and arranged that a rolling, pressure engagement is maintained between said roller means surface and said runway surfaces during relative longitudinal movement of said three members.
 10. In a device of the class described, a first rail providing longitudinal guide means and a parallel runway, a second rail providing corresponding longitudinal guide means and a corresponding runway, an intermediate member providing slide means retentively received in the guide means of both rails for relative longitudinal reciprocation, a roller journalled on said intermediate member with its periphery extending into said runways, the floor of each runway presenting a surface of one kind of material and the peripheral face of said roller presenting a surface of another kind of material, one of said materials being a fabric covered with a multiplicity of stiff little hooks and the other of said materials being a fabric covered with a multiplicity of tiny, soft loops with which such hooks retentively interengage when the two materials arE pressed together, said parts being so constructed and arranged that said roller face maintains a rolling, pressure engagement with both of said floors during relative longitudinal movement of said rails and intermediate member.
 11. The combination of claim 9 in which the surface material of said runways is the loop type while the surface material of said roller means is the hook type.
 12. The device of claim 1 in which said bridge member is secured at its opposite edges to said legs, respectively, and having an intermediate opening therethrough, a finger integral with one lateral edge of said opening and extending into said opening with its distal end free, said roller having a concentric bore whose diameter is at least equal to the width of said finger, and two substantially half-round blocks fixed to the opposite faces of said finger, respectively, the radii of said blocks, measured in directions perpendicular to said faces, being equal and, in sum, less than the diameter of said bore by approximately the thickness of said finger, said roller being sleeved on said blocks to define the journal mounting for said roller.
 13. The device of claim 12 in which said bridge member is a resiliently flexible sheet. 